What are the meanings of these idioms: have the better of us, kept us on our toes, showed his true colours, bury the hatchet, building castles in the air?

Here are the answers to the questions:

21. The idiom "have the better of us" means to overcome or control us. C) $\boxed{\text{control us}}$

22. The idiom "kept us on our toes" means to make us remain alert and ready. D) $\boxed{\text{caused us to be alert}}$

23. The idiom "showed his true colours" means to reveal one's real character. A) $\boxed{\text{revealed his real character}}$

24. The idiom "bury the hatchet" means to end a quarrel and become friends again. D) $\boxed{\text{end their quarrel and become friends again}}$

25. The idiom "building castles in the air" means to have unrealistic or impossible plans. A) $\boxed{\text{has goals that are impossible to achieve}}$